The second half of phase 5. A key now has a cost, a quota and a bill.
Rate limits use a sliding window rather than a fixed one. A fixed window lets
a caller send its whole minute's allowance in the last second of one window
and again in the first second of the next, so the observed rate is twice the
configured limit exactly when the system is least able to take it. Checking
and charging are one operation, or two concurrent requests both see room and
both take it.
Token limits are checked against an estimate, because the real count only
exists once the request has run; the difference is charged afterwards, so a
caller who consistently underestimates is still bounded, one window late. A
request with no max_tokens gets a modest assumption rather than zero —
assuming zero would let an unbounded request through every token limit.
Limits are checked before admission, not after: a request over its quota
should be refused rather than queued, where it would occupy a band's capacity
to no purpose. All refusals are 429, but a spent budget carries no Retry-After
because waiting does not help until the period rolls over, and saying
otherwise turns one client into a retry loop.
Usage goes to a buffered channel and is written in batches. Record never
blocks: if the buffer fills — a database stalled long enough to lose eight
thousand records — records are dropped and counted, because losing accounting
is bad and turning a stalled database into an outage is worse. A clean
shutdown drains what is queued; those are requests that were already served.
Failures are logged at error, since silently losing billing data is the kind
of thing discovered at the end of a month.
Requests are accounted whatever their outcome. A request that used a GPU and
then failed still used it, and a key that could spend nothing by failing would
be a way around a budget.
Budgets are counted in memory and restored from the store at startup, so a
restart does not hand every key a fresh allowance. The budget period travels
with the reservation rather than being re-derived, because a monthly budget
credited to a daily counter is a budget that never binds.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Until now anything that could reach the client port could use every model in
the catalog. A key now resolves to an identity, and that identity decides what
it may do.
Authentication wraps the whole mux rather than checking inside each handler,
so adding a route cannot add an unauthenticated one by omission. Health stays
open, because a load balancer has no key and a health check that needs one
reports the gateway down.
Nothing on the request path reads the database. A key is resolved once and
answered from memory until the entry expires; rejections are cached too, so a
client looping with a bad key cannot turn into a database read per request.
The price is that a revocation takes up to cache_ttl to take effect, which is
the trade stated in the configuration next to the knob. A store failure is
not an authentication answer: it is never cached as one and returns 503, not
401 — sending someone hunting for a key problem that does not exist wastes the
one thing an incident is short of. A revoked key is refused with the same
message as an unknown one, because saying otherwise confirms the key was real.
With auth on the band comes from the key and the band header is ignored. The
header was trusted only while there was nothing to consult, and it let any
client promote itself into the top priority band. Tenant fairness within a
band is now per key rather than per session, so one caller cannot take a band
by opening many sessions.
Allowlists are decided per model, not per string: a model's canonical name and
every alias name the same thing, so either form works in an allowlist and no
alias can reach a model that was not allowed. The first version of that test
passed without the resolution being there at all, which is why it now checks
all four combinations.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Ready replicas become router endpoints with no static configuration involved.
Endpoints that survive an update keep their live state — inflight counts,
breaker state, drain rate — so a replica that was already serving does not start
from cold because another one moved. The sink is an interface, so when the
router and control plane split into separate processes it becomes a watch stream
and nothing above it changes.
Phase 3's exit criterion now holds end to end. A node hosting a live replica is
killed while four clients stream continuously; the control plane marks it
unreachable, then lost, rebuilds the replica on a survivor and republishes.
Across three runs ~370 requests completed with zero failures and no replica was
left on the dead node. This proves the control logic, not the transport: the
agent fleet is simulated and the real path still needs the stream.
The race detector caught a genuine bug while this went in. startReplica read the
replica's fields after publishing it to the map, and scaleUp walked replica
pointers outside the lock; both raced with agent status reports, which arrive
from another goroutine and mutate exactly those fields. Against the simulated
fleet the reports came back fast enough to hit the window on every run. State is
snapshotted under the lock now and those functions work from values.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Inserted between quota checks and scheduling: admission answers when a request
may proceed, the scheduler still answers where it goes. Keeping them apart is
the point — an engine queue is FIFO and knows nothing about tenants, so once a
batch job is in it, no endpoint selection rescues the request behind it.
- saturation detector: one number per pool, the worse of queue depth and KV
occupancy, since either alone misleads.
- priority bands with per-band saturation ceilings, so the cluster degrades from
the bottom up.
- tenant round-robin within a band: one caller sending a thousand requests takes
one slot in the rotation, not a thousand.
- bounded queues with capacity (503) and TTL (504); cancelled requests leave the
queue instead of holding capacity.
- metrics for queue depth, wait time, rejections and pool saturation.
Exit criterion, measured in test/e2e: with 500 concurrent bronze requests
running continuously, interactive p99 in the platinum band stays at 1.04-1.24x
idle against a 1.5x budget. With admission off the same load pushes it to
55-60x. Both directions are asserted, so the test fails if admission regresses
and also if the load generator stops being a real load.
Two lags had to be closed, and they needed different answers. Engine metrics are
scraped and lag an interval; router inflight does not, but it counts running
requests, and treating those as queue makes a healthy engine look overloaded
every interval. What is actually queued is inflight minus batch capacity, and
capacity is not in the metric contract, so it is learned as the high-water mark
of observed running. Separately, between admission granting a request and the
router dispatching it the request is invisible everywhere, so a simultaneous
burst passed the check en masse; the controller now counts its own outstanding
leases against dispatched inflight.
One plan correction: a saturation ceiling of 1.0 was documented as "never held
back". It is not — it means "flow up to the healthy limit". A band that must
never wait needs a ceiling above 1. Plan §7.2.2 updated.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
llmgw server is real now. It fronts a static set of engine replicas with an
OpenAI-compatible API, scoring endpoints through the pipeline added in the
previous commit.
- proxy: SSE relayed event by event with a flush after each, cancellation
propagated upstream, and separate deadlines for dial, headers, first token,
inter-token idle and total. The idle watchdog is what distinguishes a wedged
engine from a slow one.
- router: dispatch with retry and model fallback. Retry only happens while
nothing has reached the client; after that, splicing two responses together
would be worse than the short stream the client already sees.
- config: YAML via koanf overlaid on defaults, with LLMGW_ env overrides.
Validation rejects duplicate endpoint ids and aliases that shadow a model,
because both misroute silently at request time rather than failing loudly.
- metrics: requests, duration, TTFT, tokens, plus per-scorer values and
per-filter drops on a separate admin listener with health and pprof.
Phase 1 exit criterion, measured in test/e2e: 1000 concurrent streams across
3 sim-engines complete at ~6800 req/s; every client disconnect frees the KV
blocks on every engine; router overhead p99 is about 0.9 ms against the plan's
2 ms budget.
The handlers live in internal/router rather than an internal/router/openai
package as the plan's tree sketched: they need the dispatch loop, and splitting
them apart would have meant an interface with exactly one implementation. Plan
§4 updated to match.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
ilkerandClaude Opus 5